Detailed explanation of PHP nl2br() function usage

PHP is a very popular programming language and has been widely used in the field of Web development. The nl2br() function is a very practical function in PHP. It can convert the newline characters in the string into the
tag in HTML, so that the newline characters can be correctly wrapped on the web page. This article will introduce the usage and precautions of this function in detail.

1. Function definition and parameters

nl2br() function is used to convert the newline character (
) in the string into the
tag in HTML. The function is defined as follows:

string nl2br ( string $string [, bool $isXhtml = true ] )

Among them, the parameter $string is the string to be converted, and the parameter $isXhtml (optional) is an optional parameter for specifying Whether to use XHTML format. If this parameter is set to true,
/ will be added to the tag, which is written as <br/>, otherwise it will not be added.

2. Function Usage

Below we will use several examples to illustrate the usage of the nl2br() function.

1. Basic usage

$original = "This is the first line.
This is the second line.";
$new = nl2br($original);
echo $new;

The output result is:

This is the first line.<br> This is the second line.

There is a newline character `
in the original string, after nl2br () function conversion becomes the newline tag
` in HTML. At this time, when the string is displayed on the web page, it will wrap correctly.

2. Using

In a form, the user may enter text that contains line breaks. If you want these line breaks to be displayed correctly on the web page, you can Use the nl2br() function.

For example, the following is a text input box:

<form action="submit.php" method="post">
  <textarea name="content"></textarea>
  <input type="submit" value="提交">
</form>

When the form is submitted, we can convert the text entered by the user into the database after being converted by the nl2br() function:

$content = nl2br($_POST['content']);

In this way, when the user visits the web page again, the text will be correctly wrapped and displayed.

3. Notes

Under normal circumstances, there is no problem using the nl2br() function. But sometimes, this function may also bring some bad effects, such as:

• In some pages with tight layout, using line breaks will make the page layout confusing.
• In some input boxes, users cannot be allowed to enter HTML tags themselves, otherwise security vulnerabilities (such as cross-site scripting attacks) may be introduced.

Therefore, when using the nl2br() function, you must pay attention to the following points:

• Use line breaks on the page as little as possible and only use them when necessary .
• In the input box, add an HTML filter to prevent users from entering malicious code.
• If you want to display text with a more complex format on a web page, you should use a rich text editor instead of using simple formatting methods such as line breaks.

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